In the field of noise or vibration control apparatus, the term "actuator" refers to a component which generates a controlled counter-vailing force and applies it to the vibrating medium, thus to reduce or eliminate the noise or vibration. Typically, actuators comprise a current-carrying coil contained in a magnetic field and driven by a current that varies with the magnitude and frequency of the vibrations to be reduced.
Depending on the specific application in which an actuator is employed, it sometimes is critical that the actuator's performance approach the maximum that can be achieved for a given actuator weight, volume, and peak force at a specified operating frequency. Today, however, the physical volume required by present actuator designs to deliver, for example, on the order of 1000 lb. peak force at a specified frequency often exceeds by far the available space for mounting the actuator. A need thus exists for an actuator with substantially improved output for a given physical volume.
A shortcoming of the magnetic circuit designs in present actuators is the existence of magnetic choke points where the magnetic flux concentrates. The resulting magnetic saturation, or choking, severely limits actuator performance potential. The performance limitations imposed by the existence of flux density concentrations particularly has impeded the development of volumetrically efficient actuators.